Production of paraffinic dinitriles, dicarboxamides or dicarboxylates by electrolytic hydrodimerization of an alpha, beta-olefinic nitrile, carboxamide or carboxylate is well known, e.g. from U.S. Pat. Nos. 3,193,475-79 and 3,193,481-83 issued July 6, 1965, to M. M. Baizer. Although the process has been sufficiently attractive that it has been in commercial use for over 9 years, efforts to develop improvements thereon have been continued with particular emphasis on lowering electric power costs and mitigatng electrode corrosion and fouling tendencies because of which it has been heretofore commercially preferable to carry out the process with a cell-dividing membrane. With the object of maintaining high electrolyte conductivity while employing a relatively low proportion of organic salts in the electrolysis medium, one approach to improvement of the process has been to carry out the electrolysis in an aqueous solution of a mixture of quaternary ammonium and alkali metal salts together with the olefinic compound to be hydrodimerized.
An example of a process utilizing such an approach is described in Netherlands Patent Application 66, 10378 which was laid open for public inspection Jan. 24, 1967. As described in that application, adiponitrile is produced by electrolyzing a neutral aqueous solution of acrylonitrile, an alkali metal salt of a polyvalent acid such as phosphoric, boric or sulfuric and a small quantity of a quaternary ammonium salt. According to the examples of that application, good selectivities can be achieved when such a process is carried out in an undivided (membraneless) cell having a graphite cathode. Further development of the process, also with use of a graphite cathode, is described in U.S. Pat. No. 3,616,321 issued Oct. 26, 1971, to A. Verheyden et al. As is known in the art, however, commercial-scale use of graphite cathodes in a process of the type discussed herein is not very attractive, primarily because graphite is quite brittle and, at the desirably-elevated hydrodimerization temperatures and generally-optimum electrolyte flow rates of at least about 0.3 meter per second, sufficiently subject to erosion and/or fouling that it soon becomes roughened and the selectivity of the reaction (which takes place at the cathode) drops sharply.
SUPERFICIALLY, IT MIGHT HAVE SEEMED THAT VARIOUS OTHER MATERIALS HAVING HIGH HYDROGEN OVERVOLTAGES COULD BE SATISFACTORILY SUBSTITUTED FOR GRAPHITE AS THE CATHODE IN ELECTROLYTIC HYDRODIMERIZATION (EHD) processes similar to that of Netherlands Application No. 66,10378 and U.S. Pat. No. 3,616,321 and, in fact, the suitability of a variety of such other materials for use in certain EHD processes has been suggested in the aforecited U.S. Pat. Nos. 3,193,375-79 and 3,193,481-83, in U.S. Pat. No. 3,511,765 issued May 12, 1970, to Fritz Beck et al. in U.S. Pat. No. 3,595,764 issued July 27, 1971, to Maomi Seko et al. and in U.S. Pat. No. 3,689,382 issued Sept. 5, 1972, to H. N. Fox et al. However, and notwithstanding those suggestions, it has been recognized in the art that at least in some instances when an olefinic compound EHD medium contains significant amounts of alkali metal salts, the selectivity with which the desired hydrodimer is produced is highly dependent on the specific cathode material employed. To illustrate, in British Pat. No. 1,014,428 issued Dec. 22, 1965, to Ivan L. Knounjants et al., the patentees demonstrated that the hydrodimer selectivity in electrolytic hydrodimerization of an olefinic compound such as acrylonitrile is quite high (70-80%) when a graphite cathode is employed with a low-temperature (below 0.degree.C.) aqueous electrolyte containing alkali metal ions in substantial concentration (0.7 to 1.2N) but that with the same electrolyte, an iron cathode yielded only about 20% of the dinitrile (based on the converted monomer) and a cadmium cathode provided practically no reaction product other than the saturated monomer (propionitrile). High ratios of propionitrile to adiponitrile obtained when various cathode materials other than graphite are employed with an electrolyte containing alkali metal ions are also demonstrated and an explanation is provided by Baizer in Journal of the Electrochemical Society, Vol. 111, No. 2, at pages 215-22 (1964).
For reasons including those set forth hereinbefore, a process by which an olefinic nitrile, carboxamide or carboxylate can be electrolytically hydrodimerized with high selectivity while using as the electrolysis medium an aqueous solution containing an alkali metal salt in significant amount and in which the cathode is dimensionally stable and resistant to corrosion for long periods of time is highly attractive for commercial use. Accordingly, the provision of such a process is a primary object of the invention described herein. Another object of this invention is to provide such a process which can be satisfactorily carried out in an electrolytic cell in which the anode is in contact with the electrolysis medium and subject to corrosion under those conditions. Further objects of the invention will be apparent from the following description and Examples in which all percentages are by weight except where otherwise noted.